1. Field of the Invention
The invention pertains to the field of digital telecommunications, and more particularly to the processing of the digital signals necessary in this type of application.
Digital telecommunications are subjected to disturbances which are due, among other reasons, to the poor quality of the transmission channel and to action by active jammers. They therefore require data to be protected efficiently.
2. Description of the Prior Art
Conventional methods associating simple error detection and a routine message-repetition procedure are advantageously replaced by the technique of error-correcting codes which introduce redundancy into the digital signals transmitted and give an effective compromise between useful flowrate and the protection of the data transmitted. In all correcting codes, there are two classes of codes in blocks which provide a reasonable balance between complexity of application and efficiency:
BCH codes based on a binary alphabet used especially to correct isolated errors;
REED-SOLOMON (RS) codes, based on an alphabet with M symbols, each having m bits, M=2m. These codes are used to correct packets of errors.
The coding and decoding operation, performed on the digital signal, makes use of the processing of polynomials with values in the Galois fields.
The French patent application No. 84 08141, filed on behalf of the Applicant and entitled "encoder-decoder of codes in blocks which can be parameterized" describes a processor specialized in this type of digital processing, comprising a polynomial operator in Galois fields. This operator performs scalar operations or polynomial operations on the elements of a Galois field chosen from among the Galois fields with 16, 32, 64 or 128 elements, making it possible to perform operations on symbols having M=4, 5, 6 or 7 bits respectively. The operator described in this application cannot be used to process data in the Galois field with 256 elements, GF(256), where the calculations are very complicated but would enable the processing of octets which are the basic symbols in data transmission. Furthermore, the structure of the prior art operator specified above cannot be used to make a fast circuit, even in the most efficient technologies of the present day. Besides, the sequences of the necessary operations can be performed only through sequences of instructions, even for operations of the type entailing the product of a polynomial by a monomial. Finally, this operator does not provide for the masking of processed data, especially for the simple location of errors.